Ruby Techniques Revealed: Autoload:

Further Googling led me to some interesting discussions about autoload . Back in December 2008, a whole group of Ruby luminaries got into a discussion about autoload's issues with threads . Turns out that even though several projects have been adopting autoload in anger recently, there are some concerns surrounding how thread safe autoload is. The proposed solution is to have a mutex between all autoloads, but I haven't yet established how far work on this (if any) has gone.